Extreme El Niño Threatens California and Southwest Winter Weather

The 2026 El Niño could bring major winter weather impacts to California and the southwestern United States as the climate phenomenon approaches unprecedented intensity, according to Weather West meteorologist Daniel Swain. By mid-October, ocean temperature measurements had reached record levels, and forecasts indicated further strengthening through late fall or early winter, potentially influencing storm activity and precipitation into 2027. Weather West reported that the event had already established record or near-record values across several major indicators of El Niño strength and position.

The measurements suggest an unusually intense warming pattern across the tropical Pacific, with potential consequences for regional weather conditions in the months ahead. The weekly Oceanic Niño Index (ONI) had reached +3.3°C, substantially exceeding the previous record of +2.1°C. The weekly Relative Oceanic Niño Index (RONI) stood at +2.4°C, slightly above the previous record of +2.3°C, while the ENSO Longitude Index (ELI) reached 191.5°E, compared with its previous record of 178.5°E.

According to Swain, major forecasting models began identifying the possibility of an exceptionally strong event months before its intensity became evident in ocean observations. He discussed the potential in April and published a dedicated Weather West report in June as confidence in the forecast increased.

California has already experienced several conditions consistent with the anticipated effects, according to Weather West. Nearshore ocean temperatures reached record levels, while much of Southern California experienced unusually high coastal humidity and humid heat during late summer. Elevated ocean water levels have also contributed to increasingly significant coastal erosion and flooding. Since July, multiple tropical storms and hurricanes have indirectly affected central and southern California, the report said.

Swain cautioned that the event's continued development does not guarantee that every seasonal forecast will prove accurate. However, he noted that observed conditions remain broadly consistent with the trajectory predicted by multi-model forecasts. The current strengthening phase involves complex interactions between tropical winds and ocean temperatures. Westerly wind bursts can temporarily cool portions of the ocean surface through evaporation, but their subsequent effects can reduce the upward movement of cooler water and push warm surface waters farther east, ultimately reinforcing El Niño.

Weather West reported that another strong westerly wind burst was underway as temperatures in the Niño 3.4 region temporarily leveled off. The wind event was expected to persist for more than two weeks and could reverse the prevailing tropical wind direction, potentially contributing to additional warming. Forecasts placed the likely peak intensity between late November and January, with December considered the most probable month.

Regional weather effects, however, typically lag behind the event's maximum intensity, meaning California and the Southwest may experience the strongest influence later in the winter. The storm-track and precipitation signals could begin emerging in November but might not become apparent until December. Once established, the pattern could persist through at least March 2027, according to the Weather West analysis.

Autumn rainfall remains difficult to predict from El Niño alone, even when the event is exceptionally strong. Weather West said October and November could still bring either relatively wet or dry conditions, with limited evidence connecting autumn precipitation directly to the event's eventual winter impacts.

For winter, the report anticipates a substantially stronger influence on California's storminess and precipitation than typically associated with weaker El Niño events. The potential for an exceptionally strong and unusually eastern-centered event distinguishes the 2026 episode from previous conditions, although the precise timing and regional severity of its effects remain uncertain.